A newly characterized chromatin insulator element isolated from the DNA of a higher eukaryotic organism and contained in vector constructs is described. The insulator element of the invention comprises a DNA sequence which contains a 5’ constitutive hypersensitive site whose functional activity and biochemical characterization as a pure insulator were previously unknown. A core DNA sequence having strong insulator activity is described. The insulator element, including the core sequence, have been demonstrated for the first time in mammalian cells to function to buffer or insulate an expressed gene from the activity of cis-acting regulatory elements, such as enhancers, in the surrounding chromatin or DNA. (US Patent 5,610,053)